Water-soluble thickener and liquid acidic detergent

ABSTRACT

A water-soluble thickener which is highly effective even in thickening strongly acidic aqueous solutions and has excellent stability in such solutions. It comprises a water-soluble copolymer having a weight-average molecular weight of 6,000,000 or higher obtainable by polymerizing a monomer mixture which comprises 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof and acrylic acid and/or a salt thereof as essential components and optionally one or more other copolymerizable monomer components including the compound represented by the following Formula (1) and/or a salt thereof, wherein the 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof represents 20 mol % or more of all the monomers.  
                 
(wherein n is an integer of 1 to 12).

TECHNICAL FIELD

The present invention relates to a thickener which is effective even inthickening strongly acidic solutions and is stable in such solutions,and to a liquid acidic detergent consisting of the thickener, which canbe used commonly in the relevant field.

BACKGROUND ART

For a detergent used to remove stains on ceramic products such asbathroom tiles, washing stands, toilet bowls, tiles for interiordecoration and the like, an acidic detergent comprising hydrochloricacid, citric acid, etc. as a cleaning component, a neutral detergent ora chlorine-based detergent has been used. Conventionally, for suchdetergents, studies are being carried out on a water-soluble thickenerwhich works effectively upon being mixed into liquid detergents tosuitably adjust the viscosity, so that when the liquid detergent isapplied on the vertical side of a tile or on a toilet bowl, the liquiddetergent flows down on the cleaning surface slowly.

For instance, among the liquid acidic detergents for cleaning tileswhich use sulfamic acid and glycolic acid in combination as acidic basematerials, an acidic detergent comprising polyvinyl alcohol as athickener and urea as a stabilizer is disclosed (JP-A-53-46302). Thisdetergent comprises sulfamic acid instead of hydrochloric acid as anacidic base material in consideration of safety. However, since sulfamicacid alone is less effective than hydrochloric acid in the cleaningeffect, the detergent uses glycolic acid as an acidic adjuvant. Further,polyvinyl alcohol as a thickener is likely to result in reducingviscosity due to the occurrence of gelation when used at lowtemperatures in winter, etc.

Further, detergents which comprise a mineral acid such as hydrochloricacid, a halogen scavenger, a surfactant and a thickener as essentialcomponents, and which comprise xanthan gum, cationized cellulose,polyethylene glycol, polyvinyl pyrrolidone or polyacrylamidemethylpropanesulfonic acid as a thickener are disclosed (for example, inJP-A-9-143498 or JP-A4-209700). Among these, a homopolymer ofpolyacrylamide methylpropanesulfonic acid shows a thickening effect tothe extent that may be obtained by 10% hydrochloric acid, but it is notsatisfactory because it cannot satisfy both the fluidity and theanti-dripping property at the same time. None of these thickeners have asufficient thickening effect under acidic conditions and satisfactorystability over time. Thus, reports have been made upon studies on usinga copolymer instead of a homopolymer as a water-soluble thickener.

For instance, reports have been made that a water-soluble thickenercomprising a copolymer comprising (meth)acrylamide alkylsulfonic acidand an alkyl group-containing unsaturated monomer (JP-A-10-279636) and awater-soluble thickener comprising a crosslinked copolymer obtained bythe polymerization of-(meth)acryl amide alkylsulfonic acid and acrosslinking monomer with (rheth)acrylic acid, dialkyl acrylamide,acryloylmorpholine, hydroxyethyl methacrylate, vinyl pyrrolidone or thelike, cause a less viscosity reduction under weakly acidic conditions orin brine solutions (JP-A-9-157130, JP-A-2001-114641, JP-A-2001-115135,etc.). These water-soluble thickeners exhibit some thickening effect andthe stability in the thickened solution over time under mildly acidicconditions which cause less irritation on the skin when used in thepharmaceutical products, the cosmetic products or the like. However,their thickening effect is unsatisfactory in strongly acidic detergentssuch as those comprising about 10% by weight of hydrochloric acid andhaving a pH value of 1 or less.

Moreover, in the processes of preparing copolymers comprisingcrosslinking monomers as described in JP-A-9-157130, JP-A-2001-114642,JP-A-2001-115135, etc., there are problems that high molecular weightwater-soluble polymers having a weight-average molecular weight of morethan 5,000,000 are used, and that since full control of the reaction isdifficult, and thus water-insoluble polymers which form a molecularstructure in the form of three-dimensional network are likely to beproduced.

As such, conventional thickeners have exhibited insufficient thickeningeffect or stability over time in strongly acidic aqueous solutions. Inan attempt to enhance the thickening effect of a detergent, animprovement such as increasing the amount of a thickener to be added maybe considered, but this causes the reduction in the fluidity of liquidacidic detergents and makes it difficult for the detergent to flow outfrom the nozzle of a detergent container, thus making it unpleasant touse the detergents. Further, detergents are produced to comprise largeamounts of organic materials, which is environmentally not preferable.Also, on the other hand, when the improvement in the fluidity of acidicdetergents is made by adjusting the amount of the thickener to be added,there is a problem in that a sufficient anti-dripping property of thedetergent on the ceramic surfaces and the like cannot be obtained.

DISCLOSURE OF THE INVENTION

The inventors have conducted extensive studies to solve theabove-mentioned problems and have found that water-soluble thickenersconsisting of certain copolymers which show excellent thickening effectand stability even in a strongly acidic aqueous solution can solve theproblems, thus completing the invention.

Thus, the present invention is characterized by the following.

(1) A first invention is a water-soluble thickener comprising awater-soluble copolymer having a weight-average molecular weight of6,000,000 or higher obtainable by polymerizing a monomer mixture whichcomprises 2-acrylamido-2-methylpropanesulfonic acid and/or a saltthereof and acrylic acid and/or a salt thereof as essential componentsand optionally other copolymerizable monomer components,

-   -   wherein 2-acrylamido-2-methylpropanesulfonic acid and/or a salt        thereof represents 20 mol % or more of all the monomers.

(2) The second invention is a liquid acidic detergent consisting of anaqueous solution which comprises the above-mentioned water-solublethickener as the essential component, and a mineral acid and/or anorganic acid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the equipment used for measuring thefluidity of a liquid acidic detergent.

FIG. 2 is a schematic diagram of the equipment used for measuring thedripping rate of a liquid acidic detergent.

REFERENCE NUMERALS

-   -   1 Stand    -   2 Nozzle of the container    -   3 Container    -   4 Beaker    -   5 Ceramic tile    -   6 Automatic pipette    -   7 Angle of inclination    -   8 Fixing grip

BEST OF CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be explained in detail.

1. Water-Soluble thickener

The water-soluble thickener of the invention is a water-solublecopolymer having a weight-average molecular weight of 6,000,000 orhigher obtainable by polymerizing a monomer mixture which comprises2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof andacrylic acid and/or a salt thereof as essential components andoptionally the compound represented by the following Formula (1) and/ora salt thereof as another copolymerizable monomer,

-   -   wherein 2-acrylamido-2-methylpropanesulfonic acid and/or a salt        thereof represents 20 mol % or more of all the monomers:    -   wherein n is an integer of 1 to 12.        1.1 2-Acrylamido-2-methylpropanesulfonic Acid

2-Acrylamido-2-methylpropanesulfonic acid and/or a salt thereofconstituting the water-soluble thickener of the invention is used toinvest with the solubility of the polymer and the viscosity to an acidicaqueous solution, and the amount thereof to be used is preferably 20 mol% or more, more preferably 20 to 60 mol %, and particularly preferably30 to 50 mol %, based on the total moles of the monomers. When theamount is less than 20 mol %, the solubility of the polymer in theacidic aqueous solution and the viscosity of the acidic aqueous solutionbecome insufficient.

The salts of 2-acrylamido-2-methylpropanesulfonic acid include, forexample, salts of alkali metals such as sodium, potassium, etc.,ammonium salts, or salts of organic amines such as triethylamine,triethanolamine, etc.

1.2 Acrylic Acid

The amount of acrylic acid and/or a salt thereof to be used, whichconstitutes the water-soluble thickener of the present invention ispreferably 80 mol % or less, more preferably 40 to 80 mol %, andparticularly preferably 50 to 70 mol %, based on the total moles of themonomers. When the amount is more than 80 mol %, the solubility of thepolymer in an acidic solution is deteriorated or the thickeningefficiency is reduced.

Further, an other copolymerizable monomer is optionally comprised in themonomer mixture, the amount of the acrylic acid and/or a salt thereof tobe used is preferably 20 to 80 mol %, and particularly preferably 35 to70 mol %, based on the total moles of the monomers. When the amount isless than 20 mol %, the dripping-preventing property is insufficient,and when the amount is more than 80 mol %, the solubility of the polymerin an acidic aqueous solution is deteriorated or the thickenability isreduced. The salts of acrylic acid include, for example, salts of alkalimetals such as sodium, potassium, etc., ammonium salts, or salts oforganic amines such as triethylamine, triethanolamine, etc.

1.3 Other Monomers

The water-soluble thickener of the present invention may comprise othercopolymerizable monomers, in addition to the above essential components,within a scope of not reducing the thickening efficiency and thestability in a strongly acidic solution, and the solubility of theobtainable copolymer a strongly acidic solution.

As such other copolymerizable monomers, mention may be made of anionicmonomers, nonionic monomers and the like, specific examples of whichinclude the following:

[A] Anionic Monomer

(Meth)acrylamide alkylalkanesulfonic acid other than2-acrylamido-2-methylpropanesulfonic acid, and an alkali metal salt orammonium salt thereof; methacrylic acid and an alkali metal salt orammonium salt thereof; maleic acid, fumaric acid, itaconic acid and thelike and an alkali metal salt thereof; and vinylsulfonic acid and analkali metal salt or ammonium salt thereof, etc.

[B] Nonionic Monomer

(Meth)acrylamides, dialkyl (meth)acrylamides such as dimethyl(meth)acrylamide, etc., hydroxyalkyl (meth)acrylates such ashydroxyethyl (meth)acrylate, etc., dialkylaminoalkyl (meth)acrylatessuch as dimethylaminoethyl (meth)acrylate, etc., dialkylaminoalkyl(meth)acrylamides such as dialkylaminopropyl (meth)acrylamide, etc.

[C] Other Monomers

Styrene, acrylionitrile, vinyl acetate, alkyl acrylate, alkylmethacrylate, vinylpyridine, vinylimidazole, allylamine, etc.

[D] Compound Represented by Formula (1)

Among the above-mentioned copolymerizable monomers, it is more preferredto use the compound represented by the following Formula (1) and/or asalt thereof:

-   -   wherein n is an integer of 1 to 12.

The compound of Formula (1) and/or a salt thereof is used to enhance theanti-dripping property of a liquid acidic detergent, but n is an integerin the range of 1 to 12, preferably 1 to 6, and more preferably 1 to 3.Even if n is more than 12, the effect is not expected to improve anyfurther, and it is not preferable because the solubility in a stronglyacidic aqueous solution is impaired. This compound may be a singlecompound with one value of n within said range, or a mixture of aplurality of the compounds with different values of n. Further, acommercially available product can be used as the compound of Formula(1), including a compound under the product name “Aronix M-5600”manufactured by Toagosei Co., Ltd., for example.

The amount of the compound of Formula (1) can be used in the range ofpreferably 0.1 to 20 mol %, and particularly preferably 0.5 to 15 mol %,based on the total moles of the monomers. When the amount is less than0.1 mol %, the effect is insufficient, while when the amount is morethan 20 mol %, any further improvement on the effect is not expected,and it is not preferable since residual monomers tend to remain.

The salts of the compound of Formula (1) include, for example, salts ofalkali metals such as sodium, potassium, etc., ammonium salts, or saltsof organic amines such as triethylamine, triethanolamine, etc.

1.4 Process for Producing a Water-Soluble Thickener

The synthesis of the water-soluble copolymer of the invention which is awater-soluble thickener may be carried out by means of gelpolymerization, aqueous polymerization, inverse suspensionpolymerization, etc. and from the viewpoint of easy increasing of themolecular weight of the polymer and easy adjusting of the polymerizationprocess or molecular weight, gel polymerization is preferred. Thepolymerization process may be a batch process or a continuous process,and a continuous process may be specifically exemplified by a continuousbelt polymerization in which an aqueous monomer solution is polymerizedcontinuously on a movable belt.

The gel polymerization process is a process employed for the productionof polymeric organic flocculant in order to obtain water-solublepolymers of very high molecular weights, and the polymers resultingtherefrom can be obtained in the form of gel.

A technical feature of the gel polymerization process is that theconcentration of the monomers in the aqueous solution is set to about 20to 50% by weight, and the amount of the polymerization initiator used isset to a trace amount, i.e., 1000 ppm by weight or less. Whenpolymerization is carried out under these conditions with the initialtemperature of the reaction solution set to 5 to 10° C., the reactionsolution is converted to a gel of high viscosity, and it becomesimpossible to carry out such operations as stirring and removal of heatof the reaction during the reaction. However, by standing the reactionsolution as such for a certain period of time, typically a maximum finaltemperature of 80 to 100° C. is reached, and polymerization is completedto yield a desired water-soluble polymer with high molecular weight.

The initial polymerization temperature for the reaction of gelpolymerization is preferably 0 to 30° C., and more preferably 5 to 20°C., and the final polymerization temperature is preferably 70 to 105°C., and more preferably 80 to 100° C. The concentration of monomers maybe adjusted so that the initial polymerization temperature and the finalpolymerization temperature fall within the ranges. Further, thepreferred polymerization time is approximately from 30 minutes to 6hours.

As the polymerization initiator, redox polymerization initiators arepreferred, and instead of using a redox polymerization initiator,radical polymerization can be carried out by irradiating an activeenergy ray such as ultraviolet ray, etc. to an aqueous monomer solutioncomprising a photopolymerization initiator.

For specific examples of a polymerization initiator, mention may be madeof salts of alkali metal persulfate such as sodium persulfate, potassiumpersulfate, etc. persulfates such as ammonium persulfate, etc., organicperoxides such as hydrogen peroxide, cumene hydroperoxide, benzoylperoxide, t-butyl peroxide, benzoyl peroxide, etc., and azo compoundssuch as 2,2′-azobis(4-cyanovaleric acid),2,2′-azobis(2-methyl-N-(2-hydroxyethyl)-propionamide,2,2′-azobisisobutyronitrile, etc. and the like. Further, in this case,it is preferable to use salts of transition metals or a salt of hydrogensulfite, reducing agents for redox formation such as L-ascorbic acidsalt), erythorbic acid (salt), amine compounds, or the like incombination.

Furthermore, the amount of the polymerization initiator added isadjusted in accordance with the type of the polymerization initiatorused, the composition, the degree of polymerization, the viscosity ofthe desired polymer, etc. Typically, it is preferable to use 5 to 10,000ppm by weight, preferably 10 to 5,000 ppm by weight, and particularly 15to 3,000 ppm by weight, based on the total amount of the monomers.

The molecular weight of the polymer is the weight-average molecularweight measured by aqueous gel permeation chromatography (hereinafter,abbreviated as GPC) using polyethylene oxide as a standard substance. Inorder to obtain a thickening effect even in a strongly acidic solution,it is necessary that the weight-average molecular weight is necessarily6,000,000 or higher. A polymer having a weight-average molecular weightof less than 6,000,000 cannot give a sufficient thickening effect.

1.5 Use

The water-soluble thickener of the present invention can be used in avariety of applications.

For example, it can be used as a thickener in neutral or weakly acidicsolutions or acidic emulsions in the applications of the pharmaceuticalproducts, the cosmetic products such as cosmetics for skin or hair,etc., building materials such as paper coating, fiber binder, etc.,fiber/paper treating agents, paints and the like.

In particular, from the viewpoint of its excellent thickening effect andstability even in a strongly acidic aqueous solution, the acidicdetergent comprising hydrochloric acid, citric acid, etc. as a cleaningcomponent is useful in removing stains on the ceramic products such asbathroom tiles, washing stand, toilet bowls, tiles for interiordecoration, etc. and the like

2. Liquid Acidic Detergent

The liquid acidic detergent of the present invention is an aqueoussolution comprising the above-described water-soluble thickener as anessential component and further comprising a mineral acid and/or anorganic acid.

2.1 Water-Soluble Thickener

The amount of the above-described water-soluble thickener comprised inthe liquid acidic detergent of the present invention varies depending onthe type of the thickener used, and the type and the amount of the acidsused in the detergent, and thus the amount cannot be determineddefinitely. However, although it is necessary to adjust the amount ofthe thickener in order to obtain the desired viscosity for variouscombinations of liquid acidic detergents in practice, the amount isgenerally preferably in the range of 0.02 to 5% by weight, and morepreferably in the range of 0.1 to 2% by weight. When the amount is lessthan 0.02% by weight, the thickening effect is insufficient, and whenthe amount is more than 5% by weight, the viscosity becomes excessivelyhigh, and the detergent may become susceptible to remain on the surfaceupon being washed with water after cleaning.

2.2 Acids

As the mineral acid or organic acid comprised in the liquid acidicdetergent of the present invention, mention may be made of mineral acidssuch as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid,etc. and organic acids such as acetic acid, citric acid, malic acid,sulfamic acid, glycolic acid, etc. These acids can be used either aloneor in combination of two or more species.

The amount of acid comprised in the liquid acidic detergent cannot bedefined definitely because different types of acid may result indifferent detergency or safety. However, the amount is preferably in therange of 3-30% by weight, and more preferably in the range of 5-20% byweight. When the amount is less than 3% by weight, the detergency isinsufficient, and when the amount is more than 30% by weight, there maybe problems in user safety or of corrosion of the periphery of theplaces of use (restrooms, bathrooms, etc.) or the like.

2.3 Others

The liquid acidic detergent of the present invention may comprisesurfactants in addition to the above-described water-soluble thickenersand acids. As the surfactants, mention may be made of anionicsurfactants such as salts of fatty acids, salts of higher alcoholsulfuric esters, salts of liquid fatty oil sulfuric esters, salts ofalkylarylsulfonic acids, etc., and nonionic surfactants such aspolyoxyethylene alkyl ethers, polyoxyethylene alkyl esters,polyoxyethylene sorbitan alkyl esters, acetylene alcohols, acetyleneglycols, etc. and the like. In addition, an antifoaming agent,preservatives, polishing agent, anti-settling agent, chelating agent,anticorrosives, perfumes may be also used in combination.

2.4 Process for Preparation of Liquid Acidic Detergents

The liquid acidic detergent of the present invention can be easilyobtained by dissolving the above-described water-soluble thickener andan acid in water. Further, water can be used as long as it is soft waterwhich does not contain alkaline earth metal ions, but it is morepreferred that the water is ion-exchanged water (deionized water).Additionally, in order to obtain the detergency, the easy handling(usability) and the stability of the liquid acidic detergent, theviscosity of the liquid acidic detergent at 20° C. is preferablyadjusted to 5 to 100 mPa·s, and particularly 10 to 20 mpa·s.

EXAMPLES

Hereinafter, the invention will be explained in more detail by means ofExamples and Comparative Examples. The terms “%” and “ppm” in thefollowing mean “% by weight” and “ppm by weight”, respectively.

Example 1

645.9 g (50 mol % equivalent) of a 50% by weight aqueous solution ofsodium 2-acrylamido-2-methylpropanesulfonate, 184.1 g (25 mol %equivalent) of a 36% by weight aqueous solution of sodium acrylate, 50.8g (25 mol % equivalent) of acrylic acid and 119.2 g of pure water weremixed to prepare 1 kg of an aqueous monomer solution at a monomerconcentration of 44% by weight. This aqueous monomer solution was placedin a Dewar flask made of stainless steel, the temperature inside thereaction vessel was cooled to 5° C., and nitrogen bubbling was carriedout for 30 minutes. Then, 10 ppm (converted in terms of the weight ofthe total amount of the monomers; hereinafter, in the same manner) oft-butyl hydroperoxide, 200 ppm of sodium persulfate and 20 ppm of sodiumerythorbate as polymerization initiators were added thereto, and thereaction mixture was left to stand for 8 hours to carry out adiabaticstationary redox polymerization. After completion of 8 hours ofreaction, thus produced water-containing gel-like polymer was removedfrom the reaction vessel and introduced into a chopper, in which thepolymer was finely cut into the form of ground meat. Thus cutwater-containing gel was dried by a hot air dryer and then furtherground by a grinder to yield a desired polymer as powders. This polymeris referred to as A1.

Example 2

916.8 g (80 mol % equivalent) of a 50% by weight aqueous solution ofsodium 2-acrylamido-2-methylpropanesulfonate, 65.2 g (10 mol %equivalent) of a 36% by weight aqueous solution of sodium acrylate and18.0 g (10 mol % equivalent) of acrylic acid were mixed to prepare 1 kgof an aqueous monomer solution at a monomer concentration of 50% byweight. This aqueous monomer solution was placed in a Dewar flask madeof stainless steel, the temperature inside the reaction vessel wascooled to 10° C., and nitrogen bubbling was carried out for 30 minutes.Then, 30 ppm of t-butyl hydroperoxide, 200 ppm of sodium persulfate and20 ppm of sodium erythorbate as polymerization initiators were addedthereto. The remainder of the procedure was carried out in the samemanner as in Example 1 to yield a desired polymer as powders. Thispolymer is referred to as A2.

Example 3

In a Dewar flask made of stainless steel as the reaction vessel, 419.4 g(30 mol % equivalent) of a 50% by weight aqueous solution of sodium2-acrylamido-2-methylpropanesulfonate, 159.3 g (20 mol % equivalent) ofa 36% by weight aqueous solution of sodium acrylate, 107.7 g (49 mol %equivalent) of acrylic acid, 5.3 g (1 mol % equivalent) of an acrylicacid dimer (product name “Aronix M-5600”; manufactured by Toagosei Co.,Ltd.) and 308.3 g of pure water were mixed to prepare 1 kg of an aqueousmonomer solution at a monomer concentration of 38% by weight. Thetemperature inside the reaction vessel was cooled to 10° C., andnitrogen bubbling was carried out for 30 minutes. Then, 30 ppm(converted in terms of the weight of the total amount of the monomers;hereinafter, in the same manner) of t-butyl hydroperoxide, 200 ppm ofsodium persulfate and 20 ppm of sodium erythorbate as polymerizationinitiators were added thereto, and the reaction mixture was left tostand for 8 hours to carry out adiabatic stationary redoxpolymerization. After completion of 8 hours of reaction, thus producedwater-containing gel-like polymer was removed from the reaction vesseland introduced into a chopper, in which the polymer was finely cut intothe form of ground meat. Thus cut water-containing gel was dried by ahot air dryer and then further ground by a grinder to yield a desiredpolymer as powders. This polymer is referred to as B1.

Example 4

432.1 g (30 mol % equivalent) of a 50% by weight aqueous solution ofsodium 2-acrylamido-2-methylpropanesulfonate, 164.2 g (20 mol %equivalent) of a 36% by weight aqueous solution of sodium acrylate, 90.5g (40 mol % equivalent) of acrylic acid, 54.3 g (10 mol % equivalent) ofan acrylic acid dimer (product name “Aronix M-5600”; manufactured byToagosei Co., Ltd.) and 258.9 g of pure water were mixed to prepare 1 kgof an aqueous monomer solution at a monomer concentration of 42% byweight. The remainder of the procedure was carried out in the samemanner as in Example 3 to yield the polymer as powders. This polymer isreferred to as B2.

Example 5

656.9 g (50 mol % equivalent) of a 50% by weight aqueous solution ofsodium 2-acrylamido-2-methylpropanesulfonate, 112.3 g (15 mol %equivalent) of a 36% by weight aqueous solution of sodium acrylate, 51.6g (25 mol % equivalent) of acrylic acid, 49.5 g (10 mol % equivalent) ofan acrylic acid dimer (product name “Aronix M-5600”; manufactured byToagosei Co., Ltd.) and 129.7 g of pure water were mixed to prepare 1 kgof an aqueous monomer solution at a monomer concentration of 47% byweight. This aqueous monomer solution was placed in a Dewar flask madeof stainless steel, and the temperature inside the reaction vessel wascooled to 5° C., and nitrogen bubbling was carried out for 30 minutes.Then, 10 ppm of t-butyl hydroperoxide, 200 ppm of sodium persulfate and20 ppm of sodium erythorbate as polymerization initiators were addedthereto. The remainder of the procedure was carried out in the samemanner as in Example 3 to yield the polymer as powders. This polymer isreferred to as B3.

Comparative Example 1

645.9 g (50 mol % equivalent) of an aqueous solution comprising 50% byweight of sodium 2-acrylamido-2-methylpropanesulfonate, 184.1 g (25 mol% equivalent) of an aqueous solution comprising 36% by weight of sodiumacrylate, 50.8 g (25 mol % equivalent) of acrylic acid and 119.2 g ofpure water were mixed to prepare 1 kg of an aqueous monomer solution ata monomer concentration of 44% by weight. Then, 500 ppm of t-butylhydroperoxide, 400 ppm of sodium persulfate and 500 ppm of sodiumerythorbate as polymerization initiators, and 1200 ppm of2-mercaptoethanol as a chain transfer agent were added thereto. Theremainder of the procedure was carried out in the same manner as inExample 1 to yield the polymer as powders. This polymer is referred toas C1.

Comparative Example 2

150.2 g (10 mol % equivalent) of a 50% by weight aqueous solution ofsodium 2-acrylamido-2-methylpropanesulfonate, 385.2 g (45 mol %equivalent) of a 36% by weight aqueous solution of sodium acrylate,106.2 g (45 mol % equivalent) of acrylic acid and 358.4 g of pure waterwere mixed to prepare 1 kg of an aqueous monomer solution at a monomerconcentration of 32% by weight. This aqueous monomer solution was placedin a Dewar flask made of stainless steel, and the temperature inside thereaction vessel was cooled to 15° C., and nitrogen bubbling was carriedout for 30 minutes. Then, 100 ppm of t-butyl hydroperoxide, 300 ppm ofsodium persulfate, 50 ppm of sodium erythorbate and 300 ppm of sodiumformate as polymerization initiators were added thereto. The remainderof the procedure was carried out in the same manner as in Example 1 toyield the polymer as powders. This polymer is referred to as C2.

[Evaluation of Properties of the Polymer]

The properties of Polymers A1 and A2, and B1 to B3 obtained fromExamples 1 to 5, and of Polymers C1 and C2 obtained from ComparativeExamples 1 and 2 were evaluated according to the procedures describedbelow. The results are presented in Table 1.

(1) Viscosity of a 0.2% by Weight Aqueous Solution

To 400 ml of pure water, 0.80 g each of the polymers obtained fromExamples 1-5 and Comparative Examples 1 and 2 were added, and thismixture was stirred for 3 hours to sufficient dissolution to prepare anaqueous polymer solution at a concentration of 0.2% by weight. Theviscosity of this aqueous polymer solution was measured by means of atype B viscometer (manufactured by Tokyo Instruments Co., Ltd.; Mode:type BM) at 30 rpm at 30° C.

(2) pH

The pH value of the aqueous polymer solution at a concentration of 0.2%by weight prepared as in the above was measured by means of a pH meter.

(3) Insoluble Portion

400 ml of the aqueous polymer solution at 0.2% by weight concentrationprepared as in the above was filtered through a standard sieve of 83mesh made of stainless steel (JIS Z 8801, inner diameter: 200 mm), andthe amount of the insoluble portion remaining on the filter wasmeasured.

(4) Weight-Average Molecular Weight

The molecular weights of the polymers obtained from Examples 1 to 5 andComparative Examples 1 and 2 were measured by aqueous GPC using anaqueous solution containing sodium sulfate (1.33 g/l) and sodiumhydroxide (0.33 g/l) as the solutes. The weight-average molecular weightwas calculated from a calibration curve obtained by using polyethyleneoxide as a reference substance. TABLE 1 Monomer Composition Viscosity ofWeight- ATBS-Na/ANa/ 0.2% aq. sol. Insoluble average Poly- AA/M-5600(30° C.) portion molecular mer [mol %] [mPa · s] pH [ml] weight A150/25/25/- 455 6.5 none 8,700,000 A2 80/10/10/- 310 6.6 none 9,500,000B1 30/20/49/1 405 5.4 none 7,500,000 B2 30/20/40/10 453 5.1 none8,400,000 B3 50/15/25/10 408 6.2 none 8,100,000 C1 50/25/25/- 16 6.5none 800,000 C2 10/45/45/- 450 6.4 none 7,800,000

The abbreviations in the Table indicate the following:

-   -   ATBS-Na: sodium 2-acrylamido-2-methylpropane sulfonate    -   A-Na: sodium acylate    -   AA: acrylic acid    -   M-5600: Aronix M-5600 (manufactured by Toagosei Co., Ltd.)    -   ATBS and Aronix M-5600 are tradenames registered by Toagosei        Co., Ltd.

Examples 6 to 19 and Comparative Examples 3 to 8

[Evaluation of Liquid Acidic Detergent]

The polymers obtained from Examples 1 to 5 and Comparative Examples 1and 2 as described above, were sufficiently stirred in a 10% by weightaqueous solution of hydrochloric acid while adopting the type ofthickener (polymer) and the concentration for application as describedin Table 2. Then, the mixture was left to stand for 2 days to produce aliquid acidic detergent having 10% by weight of hydrochloric acid.

Evaluations were carried out for the following items using each of theobtained liquid acidic detergents. The results are shown in Tables 2 to4.

(1) Viscosity: The viscosity of the liquid acidic detergent was measuredby means of a type B viscometer under the conditions of 20° C. and 60rpm.

(2) Fluidity: A commercially available container 3 made of polyethylenehaving a container nozzle 2 (opening diameter 2.4 mm) was set downwardon the stand 1, as illustrated in FIG. 1. 150 g of the liquid acidicdetergent prepared as in the above was introduced into the containerwhich had been maintained at 25° C., and the time taken for thedetergent liquid to discharge from the container nozzle 2, Tf [sec], wasrepeatedly measured three times. The average value was used to calculatethe flow rate per minute (=fluidity [g/min]) from the equation below:Fluidity[g/min]=(150[g]/Tf[sec]×60

(3) Dripping rate: As illustrated in FIG. 2, a ceramic tile 5 with alength of 15 cm on each side was set at an inclination of 17 degrees.0.30 ml of the above-prepared liquid acidic detergent was drawn with anautomatic pipette 6, and then the entire amount of the liquid acidicdetergent was dropped vertically onto the tile at a position 3 cm belowfrom the tile edge, in order to repeatedly measure the time taken forthe liquid to drip over 10 cm, Td [sec], five times. The average valuewas used to calculate the dripping distance in 10 seconds (=drippingrate [cm/1 0 sec]) from the equation below:Dripping rate[cm/10sec]=(10[m]/Td[sec]×10

(4) Solubility: The liquid acidic detergent prepared above was evaluatedfor the dissolved state of the thickener contained therein by visualobservation.

◯: It is smoothly dissolved into a clear, colorless and homogeneousliquid phase.

x: White or clear insoluble matter is observed.

xx: A large amount of white or clear insolubles are observed.

(5) Stability over time: The prepared liquid acidic detergent was sealedin a heat-resistant bottle made of borosilicate (DURAN® manufactured bySCHOTT) and was stored in a constant temperature/humidity chamber setunder the conditions of a temperature of 40° C. and a humidity of 60%.After two weeks and after one month of storage, the properties andaspects of the detergents were evaluated for the items described in theabove. The results are shown in Tables 3 and 4.

Comparative Example 9

The same evaluation as described above was performed using acommercially available liquid acidic detergent for bathroom (productname “Sanpore”: manufactured by Dainihon Jochugiku Co., Ltd., maincomponents: 9.5% by weight of hydrochloric acid, a surfactant [an alkyltrimethylammonium salt]).

Comparative Example 10

The same evaluation as described above was performed using the sameaqueous hydrochloric acid solution as the above solution, except that nothickener (polymer) was added. TABLE 2 Solubility Conc. of ViscosityFluidity Dripping rate of Type of thickener thickener (20° C.)[mPa · s][g/min] [cm/10 sec] thickener Example 6 A1 0.5% 12 109 12.7 ∘ Example 7A1 0.4% 10 119 13.8 ∘ Example 8 A1 0.3% 8 125 16.0 ∘ Example 9 A2 0.6%14 93 22.1 ∘ Example 10 A2 0.5% 12 106 24.4 ∘ Example 11 A2 0.4% 10 11826.7 ∘ Example 12 B1 0.9% 14 123 6.5 ∘ Example 13 B1 0.8% 13 127 7.4 ∘Example 14 B1 0.7% 12 132 8.0 ∘ Example 15 B2 0.9% 15 122 4.8 ∘ Example16 B2 0.8% 14 126 6.0 ∘ Example 17 B3 0.7% 18 107 6.0 ∘ Example 18 B30.6% 15 114 7.7 ∘ Example 19 B3 0.5% 13 122 9.3 ∘ Comp. Ex. 3 C1  10% 12106 44.4 ∘ Comp. Ex. 4 C1 8.0% 10 118 46.7 ∘ Comp. Ex. 5 C1 6.0% 8 12848.2 ∘ Comp. Ex. 6 C2 1.3% 9 130 22.6 xx Comp. Ex. 7 C2 1.1% 7 138 24.1x Comp. Ex. 8 C2 0.9% 6 142 26.0 x Comp. Ex. 9 alkyltrimethyl not 13 11840.0 — ammonium salt defined Comp. Ex. 10 none none 3 172 66.0 —

As shown in Table 2, the liquid acidic detergent of Examples showed goodresults as compared with those of Comparative Examples. That is,compared with Comparative Example 9, Examples 6 to 11 using polymers A1and A2 as a thickener exhibited moderate dripping rates and goodfluidity, thus resulting in liquid acidic detergents excellent in theanti-dripping property.

Further, Examples 12 to 19 using polymers B1 to B3 as a thickener alsoexhibited moderate dripping rates, thus resulting in liquid acidicdetergents excellent in the anti-dripping property. In particular, theliquid acidic detergents of Examples 15 to 19 (comprising B2 or B3) wereexcellent in the dripping rate as well as fluidity.

Meanwhile, in Comparative Examples 3 to 5 using polymer C1 having aweight-average molecular weight of 800,000, in order to obtain viscosityand fluidity values equivalent to those of Comparative Example 9, 6% ormore of the thickener was required. Further, even when the applicationconcentration was brought to 6% or higher in order to equal the fluiditywith Comparative Example 9, the dripping rate was still high, and theliquid acidic detergents were poor in the anti-dripping property.Furthermore, in Comparative Examples 6 to 8 wherein polymer C2comprising 10 mol % of ATBS-Na was used, the solubility of the thickenerwas poor, and thus the products were inappropriate as liquid acidicdetergents. TABLE 3 40° storage stability test(1) 40° storage stabilitytest(2) Viscosity (20° C.)[mPa · s] Fluidity [g/min] after after afterafter initial 2 weeks 1 month initial 2 weeks 1 month Example 6 12 12 12109 110 110 Example 7 10 10 10 119 119 120 Example 8 8 8 8 125 126 125Example 9 14 14 14 93 93 94 Example 10 12 12 12 106 107 107 Example 1110 10 10 118 118 118 Example 12 14 14 14 123 124 123 Example 13 13 13 13127 127 128 Example 14 12 12 12 132 132 132 Example 15 15 15 15 122 122122 Example 16 14 14 14 126 125 125 Example 17 18 18 18 107 107 108Example 18 15 15 15 114 115 114 Example 19 13 13 13 122 123 122 Comp.Ex. 3 12 12 12 106 106 107 Comp. Ex. 4 10 10 10 118 119 119 Comp. Ex. 58 8 8 128 129 129 Comp. Ex. 6 9 8 6 130 135 143 Comp. Ex. 7 7 6 5 138145 154 Comp. Ex. 8 6 5 4 142 150 162 Comp. Ex. 9 13 13 13 118 118 119

TABLE 4 40° storage stability test(3) 40° storage stability test(4)Dripping rate [cm/10 sec] Solubility of thickener after after afterafter initial 2 weeks 1 month initial 2 weeks 1 month Example 6 12.712.4 12.6 ∘ ∘ ∘ Example 7 13.8 13.6 13.4 ∘ ∘ ∘ Example 8 16.0 16.3 16.4∘ ∘ ∘ Example 9 22.1 22.3 22.0 ∘ ∘ ∘ Example 10 24.4 24.2 24.5 ∘ ∘ ∘Example 11 26.7 26.8 26.7 ∘ ∘ ∘ Example 12 6.5 6.1 6.3 ∘ ∘ ∘ Example 137.4 7.5 7.0 ∘ ∘ ∘ Example 14 8.0 8.3 8.2 ∘ ∘ ∘ Example 15 4.8 4.5 4.3 ∘∘ ∘ Example 16 6.0 5.8 6.2 ∘ ∘ ∘ Example 17 6.0 6.2 6.3 ∘ ∘ ∘ Example 187.7 7.8 7.7 ∘ ∘ ∘ Example 19 9.3 9.1 9.2 ∘ ∘ ∘ Comp. Ex. 3 44.4 44.444.8 ∘ ∘ ∘ Comp. Ex. 4 46.7 46.9 46.5 ∘ ∘ ∘ Comp. Ex. 5 48.2 48.7 48.4 ∘∘ ∘ Comp. Ex. 6 22.6 23.8 26.6 xx xx xx Comp. Ex. 7 24.1 27.1 28.2 x x xComp. Ex. 8 26.0 28.7 30.4 x x x Comp. Ex. 9 40.0 42.9 44.4 — — —

As shown in Tables 3 and 4, the liquid acidic detergents prepared byusing each of the polymers as a thickener were found to be such that thevalues of their viscosity, fluidity and dripping rate after two weeksand after one month were virtually not changed, and the stability wasgood.

As shown above, the liquid acidic detergents comprising water-solublethickeners which were prepared by copolymerization with appropriateweight-average molecular weights and appropriate composition ranges,showed excellent storage stability, good and suitable fluidity andanti-dripping property.

INDUSTRIAL APPLICABILITY

The water-soluble thickener of the present invention shows excellentthickening effect even in a strongly acidic aqueous solution, and theliquid acidic detergents comprising said thickener shows excellentstability and appropriate fluidity and stays suitably on the surface tobe cleaned. Thus, the liquid acidic detergent can exhibit satisfactoryusability and detergency as a detergent, thus being highly useful.

1. A water-soluble thickener comprising a water-soluble copolymer having a weight-average molecular weight of 6,000,000 or higher obtainable by polymerizing a monomer mixture which comprises 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof and acrylic acid and/or a salt thereof as essential components and optionally other copolymerizable monomer components, wherein 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof represents 20 mol % or more of all the monomers.
 2. The water-soluble thickener according to claim 1, wherein the monomer mixture comprises 20 to 60 mol % of 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof, 80 to 20 mol % of acrylic acid and/or a salt thereof, and optionally 0 to 20 mol % of the other copolymerizable monomers.
 3. The water-soluble thickener according to claim 1, wherein the monomer mixture comprises a compound represented by the following formula (1):

(wherein n is an integer of 1 to 12) and/or a salt thereof as the other copolymerizable monomer components.
 4. A liquid acidic detergent consisting of an aqueous solution which comprises a mineral acid and/or an organic acid and the water-soluble thickener according to claim
 1. 5. A liquid acidic detergent consisting of an aqueous solution which comprises 3 to 30% by weight of a mineral acid and/or an organic acid and 0.02 to 5% by weight of the water-soluble thickener according to claim
 1. 6. A thickening method comprising the step of adding the following water soluble copolymer to an acidic aqueous solution or an acidic emulsion: a water-soluble copolymer having a weight-average molecular weight of 6,000,000 or higher obtainable by polymerizing a monomer mixture which comprises 2-acrylamido-2 methylpropanesulfonic acid and/or a salt thereof and acrylic acid and/or a salt thereof as essential components and optionally other copolymerizable monomer components, wherein 2-acrylamido-2-methylpropanesulfonic acid and/or a salt thereof represents 20 mol % or more of all the monomers.
 7. The water-soluble thickener according to claim 2, wherein the monomer mixture comprises a compound represented by the following formula (1):

(wherein n is an integer of 1 to 12) and/or a salt thereof as the other copolymerizable monomer components.
 8. A liquid acidic detergent consisting of an aqueous solution which comprises a mineral acid and/or an organic acid and the water-soluble thickener according to claim
 2. 9. A liquid acidic detergent consisting of an aqueous solution which comprises a mineral acid and/or an organic acid and the water-soluble thickener according to claim
 3. 10. A liquid acidic detergent consisting of an aqueous solution which comprises a mineral acid and/or an organic acid and the water-soluble thickener according to claim
 4. 11. A liquid acidic detergent consisting of an aqueous solution which comprises 3 to 30% by weight of a mineral acid and/or an organic acid and 0.02 to 5% by weight of the water-soluble thickener according to claim
 2. 12. A liquid acidic detergent consisting of an aqueous solution which comprises 3 to 30% by weight of a mineral acid and/or an organic acid and 0.02 to 5% by weight of the water-soluble thickener according to claim
 3. 13. A liquid acidic detergent consisting of an aqueous solution which comprises 3 to 30% by weight of a mineral acid and/or an organic acid and 0.02 to 5% by weight of the water-soluble thickener according to claim
 4. 